JPS61100683A - High speed neutron detector - Google Patents

Abstract

PURPOSE:To enable the real time measurement of neutron energy, by measuring neutron energy by the number of layers of a plastic scintillator through which a recoil proton passes. CONSTITUTION:A neutron detection part is constituted by alternately laminating plastic scintillator each having a thickness of about 0.5mm and reflective films each with a thickness of about 0.1mum comprising a metal or dielectric material multi-layered film. One detection element is constituted of one plastic scintillator 1 and the reflective films 2 provided to both sides thereof. Neutron incident in parallel to the laminated direction expeles the hydrogen atom nucleus constituting the plastic scintillator 1 to generate a recoil proton. By measuring the number of layers of the plastic scintillator 1 through which the recoil proton was passed, only the neutron flux of 14 MeV in the neutron generated in a nuclear fusion reactor can be measured in a real time.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a 14 MeV system used for power control of a nuclear fusion reactor.
This relates to fast neutron detectors.

[Background of the invention]

Conventionally, in laboratories, plastic scintillators have been used to detect fast neutrons.

Since the energy of recoil protons generated by a neutron with energy E is distributed with equal probability between 0 and Ea, in the conventional method, the neutron energy is determined by numerical calculation from the measurement results. Therefore, it is difficult to measure neutron energy in real time, and it cannot be used to control the output of a fusion reactor. Neutron energy measurement using a plastic scintillator is described in Section 15.3.2 of Radiation Measurement Handbook (1982), published by Nikkan Kogyo Shimbun.

[Purpose of the invention]

An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide a fast neutron detector that can be used to control the reactor power of a nuclear fusion reactor.

[Summary of the invention]

The present invention has a recoil proton detection section with a laminated structure of a plastic scintillator and a reflective film, and enables real-time measurement of neutron energy by discriminating energy based on the number of layers of the plastic scintillator through which the recoil protons have passed. It is.

[Embodiments of the invention]

The present invention will be explained in detail by way of examples. FIG. 1 is an overall configuration diagram showing an embodiment of the present invention. In the figure, 1
is a plastic scintillator, 2 is a reflective film, 3 is a microchannel plate, 4 is an anode, 5 is an insulating substrate,
6 is an amplifier, 7 is a comparator, 8 is a latch circuit, 9 is a controller, 10 is a multiplexer, 11 is a digital trigger pull 1 shot, 12 is a pulse width measuring circuit, and 13 is an OR circuit.

The neutron detection part consists of a plastic scintillator 1 with a thickness of 0.5 mm and a metal or dielectric multilayer film with a thickness of 0.1 mm.
Reflective films 2 of .mu.m are laminated alternately. One detection element is composed of one plastic scintillator 1 and reflective films 2 on both sides. 14Me incident parallel to the stacking direction
The neutrons of V repel the hydrogen nuclei constituting the plastic scintillator 1 and generate recoil protons. The energy ER of recoil protons has the following relationship with the scattering angle θ.

B a 1IllE cos” #
-"=' (1) The maximum energy of a recoil proton is equal to the neutron energy E, and the range of a 14 MeV recoil proton in the plastic scintillator 1 is 3 mm. The energy and range of a recoil proton are proportional Considering that,
Number of passing plastic scintillators 1 nJ'i', n = a cos''#/a =-=(
2). d is the thickness of the plastic scintillator 1. Therefore, the number of plastic scintillators 1 through which 14 MeV recoil protons pass is six.

The scattering angle for n = 5 is 20° from equation (2).

? The energy ER at that time is 0.9 E. Therefore, considering that the energy distribution of recoil protons is a rectangular distribution, the probability that signals are detected simultaneously by six plastic scintillators 1 is a factor of 10, and the neutron flux can be calculated backwards from this. n.

If a neutron of 14 MeV is detected when = 6, the energy resolution in this case is 0.1E, Zl, 4MeV
It is. In the case of a nuclear fusion reactor, in addition to 14 M e V, 2.
Although there are neutrons of 5 M e V and r-rays of several MeV, they can be sufficiently distinguished from each other based on the above energy resolution. Therefore, by measuring the number of simultaneous outputs from the six plastic scintillators 1, the neutron flux of 14 MeV can be determined.

The energy lost by a recoil proton of 14 M e V in one plastic scintillator 1 is approximately Z 3 M e V
It is. Since one photon is emitted with the energy loss of I K e V, 2300 photons are generated in one detection element due to the passage of recoil protons. If the reflectance of the reflective films 2 on both sides of the plastic scintillator 1 is 95, approximately 20 photons, ie, 460 photons, are incident on the microchannel plate (CMCP) 3. MCPFi
, a plate-like structure made by bundling thin glass tubes that perform the same role as a photomultiplier tube, and the input end and output end correspond one-to-one. Photons incident on the MCP are converted into photoelectrons at the input end.

It is amplified about 10' times. The conversion efficiency to photoelectrons is 1
04, the number of electrons at the output end is 4.6
The number is approximately 10', which is sufficiently detectable.

The anode provided on the insulating substrate faces the plastic scintillator 1 with the MOP in between, and its shape is as follows:
It is the same shape as the MCP side of the plastic scintillator. As a result, the fluorescent light generated within the plastic scintillator 1 is detected by the corresponding anode and sent to the next signal processing circuit.

The charge collected by the anode 4 is converted into a pulse voltage by an amplifier 6, and then a comparator 7 discriminates pulses having a set voltage or higher. The set voltage is set to about 115 times the pulse voltage caused by recoil protons so as to exclude the pulse voltage caused by r-rays. The latch circuit 8 is set to O by a signal from the controller 9 at the start of measurement or at the end of reading out the contents of the latch circuit 8. A signal due to recoil protons is detected, and 1 of the latch circuit 8
When becomes 1, the output of the OR circuit 13 becomes 1.

Upon receiving this signal, the controller 9 blocks the launch circuit 8 from receiving the signal after 100 ns. At the same time, a signal is sent to the multiplexer 10 and the information recorded in the launch circuit 8 is sequentially read out. Simultaneously with the completion of reading, the controller 9 sets the trigger circuit 8 to O and starts the next measurement.

By making the pulse width f of the retriggerable one shot 11 a little longer than the pulse width of the multiplexer 10, as shown in FIG. A running force with a range of width can be obtained. Among its outputs, 1 triggerable shot 1
The one with a pulse width 6 times the pulse width t of 1 is 14M
This corresponds to the output of eV neutrons. The pulse width measurement circuit 12 measures the width of the output pulse from the triggerable 1 shot 11, and outputs an output when a pulse six times the pulse width τ is detected. Since this pulse corresponds to 14 MeV neutrons, the neutron flux can be determined from K by counting the number of pulses.

FIG. 3 is a block diagram showing one embodiment of the pulse width measurement circuit 12. In the figure, 14 is one shot at rise, 15
16 is a clock circuit, 17 is a counter, 18 is a delay circuit, and 19 is one shot at a rising edge. When the pulse train shown in FIG. 2 is input, a measurement start pulse for the counter is output from the rising edge 14 at the rising edge of the input pulse. The color/receiver 17 thereby starts counting the clock pulses from the clock circuit 16 and ends the counting by the pulse from the falling shot 15 which is output in response to the falling edge of the input pulse. When the pulse width of the clock circuit 16 is set to f/10, 1
The pulse count corresponding to neutrons of 4 M e V is
It will be 51-60.

Therefore, when the content of the counter reaches 55, 1 at the rising edge.
By outputting pulses from shot 19, 14M
It is possible to detect eV neutrons. At the time of falling, the pulse of one shot 15 is delayed by about 1 ions by the delay circuit 18, the counter 17 is reset by the pulse, and waits until the next counting start signal.

〔Effect of the invention〕

As explained above, according to the present invention, by measuring the neutron energy by the number of layers of the plastic scintillator through which the recoil protons pass, only the neutron flux of 14 M e V of the neutrons generated in the fusion reactor can be realized. It can be measured in hours. Therefore, by using such a fast neutron detector, it is possible to control the output of a fusion reactor, which has a large effect on improving operational reliability.

[Brief explanation of drawings]

Fig. 1 is an overall configuration diagram showing an embodiment of the present invention, Fig. 2 is a diagram of output signal formation from a retrigger pull-l shot whose pulse width is proportional to recoil proton energy, and Fig. 3 is a pulse width measurement diagram. FIG. 2 is a block diagram showing an example of a circuit. 2... Reflective film, 4... Anode, 5... Insulating base, 6... Amplifier, 7... Comparator, 8... Latch circuit, 9... Controller, 10...・Multiplexer, 12
... Norculus width measurement circuit, 13... OR circuit.

Claims (1)

[Claims] 1. A neutron detection section consisting of alternating layers of plastic scintillators and light reflection films, a microchannel plate installed on one side parallel to the stacking direction, and an anode of the same shape as the microchannel plate side of the plastic scintillator with each plastic scintillator. An electron detector that amplifies and detects the output of the light receiving unit and each anode installed on the output side of the microchannel plate, and generates a neutron detection pulse when there is simultaneous output from a certain number of continuous anodes. A fast neutron detector characterized by consisting of a circuit.